Neural tube-neural crest
Neural tube-brain & spinal cord
Neural crest-most components of PNS
-non-neural component in the body and head.
Fundamental processes in Nervous system
formation
•Induction-Proliferation
•Migration-Differentiation
•Pattern formation
•Intercellular communication
•Stabilization or Elimination
•Development of integrated pattern
Changes in Gross Structure of NS•Closure of neural tube
24th-day -cranial neuropore 26th-day -caudal neuropore
•Cephalic end-primary brain vesicles
-procencephalon-mesencephalon-rhombencephalon•Spinal cord
3-wk. Embryo : - C shape - cephalic flexure (mesencephalon) - cervical flexure (hind brain&spinal cord)
5-wk. Embryo : - procencephalon-Telen., Dien.
-mesencephalon
-rhombencephalon-Meten., Myelen.
A-lateral view of the brain vesicles and part of spinal cord. B-diagram showing the cavities of the three brain vesicles and spinal cord
Diencephalon - optic vesicles
Mesencephalon - sharply bend by cephalic flexureRhombencephalon - Pontine flexure thin roof
Histogenesis within Nervous System
•2 major cell lineages
- Neuronal progenitor cell neurons
- Glial progenitor cell
astrocyte, oligodrendrocyte,
ependyma (neural tube)*Microglia-enter CNS from outside
Neuron-large cell body
-long processe
-axon-carry signals to
targets
-dendrites-receive input
Neurons need to “ reach out and touch “ each other by forming synapses to survive.
Formation of Zones
1. Ventricular zone-ependymal cellsbecome epithelial lining of central canal
2. Mantle zone-neuroblast cellsbecome gray matter of the CNS
3. Marginal zone-neuronal processesbecome white matter of the CNS
Formation of zones & fundamental organization of the developing neural tube
Note:
-ependymal zone
-mantle zone
-marginal zone
<---Sulcus limitans
Fundamental Organization of Neural
tubeDorsal portion/Alar plate/sensory
Ventral portion/Basal plate/motorRoof plate - Floor plate
Spinal cord formation
** Basic plan of neural tube is preserved in spinal cord
**•Mantle zone = H-shape of gray matter with central canal
•Marginal zone = White matter -->>myelinated nerve fibers
Spinal cord - PNS
•Neuroblasts of basal plate ->> outgrowth of axons -->ventral nerve root
•Thin processes of neuroblast of spinal ganglion-->dorsal nerve root
Dorsal aspect
Ventral aspect
Development of a peripheral nerve
A-showing motor axon, growing fiber of nerve cell in DRG. B-showing ventral motor and dorsal sensory root joining to form the trunk of spinal nerve
Gross change of spinal cord•6-wk.-->full length of vertebral
column•8-wk.-->end ~Co4•14-wk.-->end ~S1•23-wk.-->end ~L4•Birth-->end ~L3•Adult--> end~L2-3-filum terminale &cauda equina
Functional components
•2 functional categories: -GSA(soma,body) & GVA(viscera)
Dorsal alar horn = Afferent neurons
Ventral basal horn =Efferent neurons•2 functional categories: GSE & GVE
Brain Formation
•The original organization of neural tube is altered in the formation of many regions of the brain.•Nerve cells form concentrated collections called nuclei in the brain
•Dilatations of the central lumen form ventricles in the brain
-lateral ventricle-> Telen.
-third ventricle-> Dien.
-cerebral aqueduct-> Midbrain
-fourth ventricle-> Hindbrain* CSF - choroid plexus
Development of the ventricular system of the brain
A-early embryo B-during expansion of cerebral hemisphere C-postnatal morphology of ventricular system
A
Formation of specific brain regions
Rhombencephalon - Metencephalon
- MyelencephalonMedulla oblongata-transitional zone
*-major alteration --> 4th ventricle
Basal plate&Alar plate in brainstem
Expansion of roof plate- 4th ventricle
Basal plate-->close to midline
Alar plate--> lateral
<---Sulcus limitans
Alar and basal plates in myelencephalon showing the position of nuclear groups at different stages of development
Basal plate contains three motor nuclei
-medial somatic efferent gr.=SE
-intermediate special visceral efferent gr.=SVE
-lateral general visceral efferent gr.=GVE
Alar plate contains sensory nuclei*-most lateral
special somatic afferent gr.=SSA
general somatic afferent gr.=GSA *-intermediate
special visceral afferent gr.=SVA *-medial general visceral afferent gr.=GVA
Brain Formation
Hindbrain-meten.-->pons&cerebellum
Pons contains - fiber tracts
- cranial nerve nuclei
- pontine nuclei
Cranial end of hindbrain (meten.)expands outwards to f ormcerebellum.
Cerebellum - specialization of alarplates --> Rhombic lips
Two cerebellar hemispheres+Vermis
The development of the cerebellum.- Dorsal view
Note: 3 apertures - Foramen of Magendie(1-median)
-Foramen of Luschka(2-lateral)
Formation of the cerebellum or cerebrum involves formation of multiple neuronal layers in the cortex
There is a second wave of proliferation fron the inner ventricular layer-->Germinal layer and give rise to cerebellar cortex
Glia play an important role in migration of cortical neurons
Radial glia-->for guidance neurons to their destination
The external cortical neurons-layers * The cerebellar hemispheres undergo extensive folding = Folia
Radial glial cells and their association with peripherally migrating neurons during development of the brain
Mesencephalon
The alar region forms 4 swellings called corpora quadrigemina
The ventral region forms
-gray matter in tegmentum
-white matter in cerebral peduncles
Tegmentum -cranial motor nuclei
-2 prominent relay nuclei=red nucleus
& substantia nigra
Colliculi =relay nuclei for auditory & visual systems
Cerebral peduncle=fiber tracts from cerebrum > cerebellum > spinal cord
Forebrain-->dien. & telencephalonDien. forms midline brainstem regions from its alar plate-contain relay nuclei.
Dorsal -thalamus & epithalamus
Ventral -hypothalamus
Medial surface & X-section of prosencephalon. Note:corpus striatum bulge from the floor of lateral ventricle
A -medial surface of telencephalon & diencephalon
B -X-section
Note:thalamus,hypothalamus & corpus striatum
*Craniopharyngioma-remnant of Rathke’s pouch
Midline -epiphysis
Pituitary gl.-downgrowth of hypotha. + upgrowth of pharyngeal ectoderm
Functions
Thalamus-relay center for cerebral cortex
Epithalamus -olfactory input
Pineal gl.-extension of epithalamus
*-neurosecretory cell-->melatonin
Hypothalamus-receiving input from many CNS areas.
-regulates autonomic visceral fn. including sleep,body temp.,digestion
-regulates endocrine secretions of pituitary gland
Telencephalon forms the cerebral hemispheres by bilateral expansionCerebral cortex-waves of migration to form cerebral cortex=neocortex
-intermediate zone-->white matter *Forming multiple synaptic connections is important to the development of the brain*
*The cerebral hemispheres fold into lobes and gyri->begin 14 weeks
Fetal period-frontal,parietal, temporal and occipital lobes
Sulcus/sulci separate some lobesConvolutions - gyrus/gyri
-begin betw.6&8months
Showing the development of gyri and sulci on the lateral surface of the cerebral hemisphere
A=7 months B=9 months
Corpus striatum formation
•At the base of telencephalic vesicle
•Dorsal to the thalamus
C -shaped corpus striatum
-caudate nucleus
-lentiform nucleus
A -medial surface of telencephalon & diencephalon
B -X-section
Note:corpus striatum -caudate&lentiform nucleus
-internal capsule
Commissures
**Lamina terminalis** •1st - antr commissure
•2nd- hippocampal commissure
•3rd - corpus callosum-biggest
-postr & habenular commissures
(pineal gland) -optic chiasm
Meninges form a protective coating around the entire CNS
Meninges -3 layers of CNT
1. Tough outer coat = Dura mater
2. Middle layer = Arachnoid mater
3. Inner layer = Pia mater
Subarachnoid space is filled with CSF, forming a protective cushion for the brain.
CSF Lat. ventricle
3rdventricle
Cerebral aqueduct
4thventricle
Foramen of Magendie
Foramen of Luschka
B-showing the lateral and medial apertures in the roof of the 4th
ventricle
Development of the ventricular system of the brain
Outer dura - mesoderm surrounding neural tube
Arachnoid & Pia-cranial
neural crest cells
-caudal
mesoderm
Meninges
from 2 sources
Congenital defects of the CNS
•Mental retardation-no detectable brain abnormality
•Gross morphological defects
-spina bifida/occulta/cystica-meningocele/
meningomyelocele /meningoencephalocele-rachischisis
PNS development
PNS consists of the neural tissue outside CNS•ganglion/ganglia-neurons•peripheral nerve-nerve cell process
Neural crest forms most of the PNS
Neural crest
Neural crest forms most of the PNS
Two types of ganglia
sensory ganglia
autonomic motor ganglia